The present invention relates to a stretchable stripwound hose, and to a rigid or flexible conduit including such a stripwound hose, especially for application in exhaust pipes of motor vehicles.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Stripwound hoses are typically made of metal and oftentimes used in decoupling elements for exhaust systems of motor vehicles. For example, German Patent Document DE 10 2007 016 784 A1 describes a singly hooked stripwound hose which enables an axial stretch of up to 70%. By definition, the term stretch relates to the lengthening of the stripwound hose in percentage from a fully compressed state (length Lmin) to the fully stretched state (length Lmax), i.e. stretch=(Lmax−Lmin)/Lmin. The attainable stretch disclosed in this document is, however, still inadequate, especially in situations of encased curved conduits having tight radii of curvature.
Stripwound hoses are used as liners in particular in the automotive field, such as passenger cars or utility vehicles, for exhaust ducting in decoupling elements of exhaust systems. The stripwound hoses are installed in gastight metal bellows to avoid additional turbulence in the exhaust flow and to improve thermal and acoustic insulation properties of the decoupling element.
In utility vehicles, the stripwound hoses are frequently used separately and attached as decoupling element in exhaust systems in the absence of an enveloping metal bellows. In view of a slight but still admissible residual leakage, the need for a gastight casing is in many cases not required. An example of a metal hose used as decoupling element is the so-called agraffe hose. All conventional stripwound hoses are multilayered but generally made from a single metal strip that is initially flat.
As regulations worldwide with respect to emission of harmful substances will become more stringent in the future, exhaust systems are increasingly equipped with aftertreatment modules such as, e.g., soot particulate filters and SCR systems. The operativeness of aftertreatments of exhaust systems is dependent on the temperature of the exhaust undergoing the aftertreatment. This applies in the case of SCR systems for the catalytic reaction which should result in an almost complete reduction of nitrogen oxide shortly after startup. When a particulate filter is involved, passive regeneration can occur only when the minimum exhaust temperature is exceeded. The active regeneration, e.g. initiated through injection of unburnt diesel in the exhaust system, also works more efficient with increasing exhaust temperatures. As a result, there is a demand to minimize temperature losses of the exhaust during its flow from the turbocharger outlet to the after treatment.
This demand applies to all components of the exhaust pipe, including straight and curved pipe sections and in many cases a flexible conduit. All these components should ideally be thermally insulated. In the case of passenger cars, insulation is realized by so-called airgap insulation. In other words, the exhaust pipes disposed directly downstream of the engine up to the catalytic converter are double-walled. As an alternative, the placement of screening sheets onto a single-walled exhaust pipe has also been proposed.
In utility vehicles, flexible conduits are typically provided with airgap insulation. Rigid pipelines, especially bent pipes, on the other hand, are normally not double-walled because bending of double-walled pipe in the relevant diameter zone of 77 mm up to 140 mm is complicated and difficult. The reason being that the industrial standard requires in this diameter zone smallest bending radii of 1*D (bending radius=pipe diameter) so that in most cases only a single-walled pipe can be reliably used. As a consequence, insulations are normally manually applied after the exhaust ducting of utility vehicles has been finished through welding. Oftentimes, prefabricated insulation pads are wound about the pipes or E-glass fabrics are attached onto the straight and curved pipe section underneath a hermetically welded lining of thin, preformed metal sheets. This is complicated and goes against a standardization and industrialization of attaching thermal insulations. Standardization and industrialization are desired because in the future most of exhaust ducting between turbocharger outlet and entry into the aftertreatment has a thermal insulation.
A multilayer configuration and implementation of an airgap insulation can be realized by enclosing a rigid exhaust pipe with a stripwound hose. However, the bending radii of the curved pipes of up to 1*D (bending radius=pipe diameter) limits this application. Realization of such small bending radii cannot be attained with conventional agraffe-type stripwound hoses because of the stretch limitation of about 35%.
It would therefore be desirable and advantageous to provide an improved stripwound hose to obviate prior art shortcomings.